1. Field of the Invention
The present invention relates to inventory control systems, and in particular, to RFID tracking and monitoring of stored items. More specifically it relates to tracking and storage of items, for example vials containing biological material, stored within a low temperature environment in for example a freezer using RFID tags.
2. Related Art
Inventory management and control systems are used to track and monitor an inventory of stored items. In such systems each stored article may be assigned a unique identification number. A database is then used to track the location of the item using the unique identification number to identify each article. In more sophisticated systems the unique identification number may be encoded onto a radio frequency identification (RFID) tag which is attached to the article. The RFID tag when excited and interrogated by a radio frequency interrogation signal of the correct frequency will then resonate and be inductively coupled to transmitted a radio frequency signal including the unique identification number encoded on the RFID tag. This can then be received by a radio frequency receiver and reader connected to the database to automatically identify and record the presence of the RFID tag and article with that unique ID without manually entering the ID number. Such systems are well known and provide a convenient automatic way to identify and then track and monitor various stored items.
Examples of various prior inventory management and control systems for monitoring stored items, including items stored in freezers and fridges, using RFID tags on the times and RFID tag reader arrangements are described in: EP 1793326; US 2005/0247782; U.S. Pat. No. 6,982,640; US 2003/0174099; and WO 2007/024540; EP1703435, EP 1814059 and GB 2433385 also describe particular RFID tag reader arrangements, which could be used in such inventory management systems. Typically in these systems a single RFID reader is connected to multiple antennas via various switching arrangements. The multiple antennas provide a larger range and area of coverage as well as target specific ranges. Specifically the switches allow connection to each respective antenna which operates over a localised region and area to thereby allow targeted reception and interrogation, as well as allowing wider coverage with less power than would be required from a single antenna designed to operate over the entire area. The switches operate to connect the different antenna and interrogate and power the RFID tags within the respective different antenna reception areas until they are all read. Each antenna area is connected and the tags interrogated, before then switching to the next antenna to read the tags covered by that antenna. The switches in these systems simply switch and connect to different antennas and particular areas.
Some articles may need to be stored and kept at very low temperatures, for example at approximately −80° C., and within freezer units. In particular it is often necessary to store biological samples and products a such low temperatures within suitable freezer units. It may furthermore be particularly important to accurately and securely track and monitor such stored biological items. However while RFID tag systems can be used, conventional RFID tags and inventory monitoring systems are generally only specified to operate down to −40° C., and are not considered in the art to be suitable to operate at such low temperatures (eg. −80° C.) at which such articles may be stored. Indeed operating such convention systems at such low temperatures has proved problematic and unreliable. Accordingly other, less reliable, and advantageous systems have to be used to track and monitor such stored items.
Another problem with RFID tag systems, in particular when used to monitor multiple items stored in a confined environment and in very close proximity to each other, is of interference between the signals from the tags such that the individual signals and identification numbers of the individual tags cannot be received and read. In addition the reader should ideally be matched to the inductive resonant load. However a large and varying number of tags, depending on number of items stored, will alter the inductive resonant load on the reader. Such problems are particularly problematic for items stored within a freezer where a large number of items may be stored within the confined environment of the freezer, and are furthermore shielded by the outer, generally metallic, casing of the freezer which further interferes with the RF signals.
It is therefore desirable to provide an improved system which addresses the above described problems and/or which offers improvements or an alternative to existing arrangements generally. In particular it is desirable to provide an improved RFID monitoring system which can operate at low temperatures. It is also desirable to provide an improved RFID monitoring system that can monitor a large number of items stored within a confined environment, and which is less susceptible to interference. Furthermore it is desirable to provide an improved integrated low temperature storage and monitoring system.